Strömkryptografiska

Strömkryptografiska, also known as stream ciphers, are a type of symmetric encryption algorithm. Unlike block ciphers which encrypt data in fixed-size blocks, stream ciphers encrypt data one bit or byte at a time. This is achieved by generating a pseudorandom keystream which is then combined with the plaintext using a simple XOR operation. The keystream generator is initialized with a secret key and often a nonce or initialization vector.

The core principle of a stream cipher is the generation of a pseudorandom sequence that is computationally indistinguishable from a truly random sequence. This keystream is then XORed with the plaintext to produce the ciphertext. Decryption is performed by XORing the ciphertext with the same keystream, which recovers the original plaintext. The security of a stream cipher relies heavily on the unpredictability of its keystream. If the keystream can be predicted or if the same keystream is reused with different plaintexts, the cipher becomes vulnerable.

Stream ciphers are often chosen for applications where data arrives in a continuous stream, such as real-time communication protocols or wireless transmissions. They can be more efficient than block ciphers in these scenarios due to their bit-by-bit processing, which can lead to lower latency and simpler hardware implementations. However, careful implementation is crucial to avoid security pitfalls. Common examples of stream ciphers include RC4 (though now considered insecure for most applications) and ChaCha20, which is widely used in modern TLS implementations. The security of stream ciphers has been a subject of extensive research, with a constant effort to develop new, more robust algorithms.